FIG. 1 is a perspective drawing of a prior art swing stool table 100. The table comprises a horizontal top 102, one or more vertical posts 104, a longitudinal support beam 106, one or more swing stools 108 and one or more footplates 110. The swing stools each comprise a lateral bracket 112 mounted to the beam, a pivot bolt 116 forming a hinge, an arm 114 extending horizontally from the bolt, and a seat 118 mounted on the distal end of the arm. When not in use, the arm may be rotated about the bolt so that the seat rests adjacent to the beam and under the top of the table. When in use, the arm may be swung out 132 so that the seat extends laterally away from the top of the table and a person can sit on it. The top, posts, plates, brackets and arms are all made of steel or cast iron. The beam and seats are made of wood.
In order for the table to be steady, it must be designed so that the outward tipping torque 160 about the lateral edge 154 of the footplates 110 is negative (i.e. the net torque is holding the table down). This must be true when all of the seats on one side of the table are swung out and occupied by heavier-than-average people and all of the seats on the opposite side are folded in and not occupied. The net torque can be calculated by summing the torque due to the weight of the table and the torque due to the weight of the persons occupying the seats. The torque of the table is determined from the table weight 162 and the lateral distance from the table center of mass 163 to the lateral edge of the plates when the seats on the distal side of the table are folded in and the seats on the proximal side of the table are folded out. This distance is equal to the difference between the lateral plate extension 152 from the longitudinal centerline 120 of the table and the center of mass lateral offset 164 from the longitudinal centerline of the table. The table center of mass is laterally offset from the longitudinal centerline of the table because the seats on the proximal side are swung out and the seats on the distal side are folded in.
The torque of a person occupying a seat can be calculated from the weight of the persons 166 and the lateral extension 134 of the center of the seat 136 from the longitudinal centerline of the table 120 minus the lateral plate extension 152. As used herein, the “center of a seat” is the position where the center of mass of a person sitting in a seat would be. For circular seats, this is about where the geometric center of the seat is. For non-circular seats, it may be where the seat is designed for a person to sit (e.g. a formed area). In the illustrated prior art design, the table weight is about 272.4 kg. The top lateral extension 122 and the plate lateral extension are both about 38.1 cm. The seat lateral extension is about 52.1 cm. The plate extension is about the same as the top extension so that the plates do not extend laterally past the top lateral edge 124 of the table. This makes the table easier to ship when assembled. The prior art design allows for three larger than normal individuals each weighing 181 kg to sit on one side of the table without tipping. The table would tip, however, if the table mass was less.
FIG. 2 is a perspective drawing of the swing stool 132 of FIG. 1 after it has been swung out. The stool comprises a lateral bracket 112 mounted to the longitudinal beam 106. A hinge connection to the arm 114 is formed by the vertical pivot bolt 116. The distal end of the arm comprises a horizontal seat plate 220 (not visible in this drawing). The seat 118 is attached to the seat plate. The arm has a generally bent “I” beam shape comprising a top flange 202, bottom flange 204 and web 210. An opening 212 is provided in the web to reduce weight. The proximal end of the arm comprises a vertical end flange 216. A vertical end fillet 214 is provided on both sides of the web and the outward face of the end flange to strengthen the arm against twisting 206 when a person sits in the seat.
The proximal end of the top flange further comprises a horizontal top disk 217). The proximal end of the bottom flange comprises a horizontal bottom disk 218. Corresponding disks are provided on top 232 and bottom 234 flanges of the bracket. The bracket also has a generally “I” beam shape with top and bottom flanges, webs and an opening in the web. Holes are provided in the centers of the disks for the pivot bolt to pass through to form a hinge.
The top and bottom flanges of the arm extend outwardly and bend both laterally 222 and upwardly 224 relative to the bracket 112 to join together at the distal end of the arm. The seat plate is mounted horizontally on said distal end of the arm. The bend in the arm is provided so that a person, such as a woman wearing a skirt, may sit on the stool without having to raise a leg over the arm. The bend in the arm, however, causes a significant twisting torque 206 about the longitudinal centerline 236 of the bracket when a person sits on the seat. This can cause sag 208 in the distal end of the arm. When the arm is made from ductile cast iron, the sag is calculated to be about 2.5 mm for a 181 kg person. This is acceptable sag. The twisting torque also produces significant stresses in the arm. The maximum stress for a 181 kg person is calculated to be about 89 Mpa. The yield strength of ductile cast iron is about 551 Mpa. Thus there is about a 6× safety factor in the yield strength versus the maximum expected stresses. Safety factors of 2× or greater are considered acceptable.
One of the disadvantages of the prior art design is the large weight of the table. This large weight is required so that the table will not tip over when larger than average persons all sit on one side of the table. The high table weight makes the table unsuitable for most home use. It is also too heavy to be provided in a kit form for an average homeowner or apartment resident to take home and assemble.
The weight of the table can be reduced by using lower weight metals in the swing stools. The design of the arm and bracket, however, must be changed or the seat will have too much sag. The stresses in the arm might also exceed the yield strength of the lighter weight metals. Furthermore, a lower weight table with the prior art design will no longer be stable with several large persons sitting on one side and no one sitting on the other side. Thus there is a need for an improved seat design suitable for lighter material construction, an improved table design that the table is stable for sitting, and a kit design for the table that is suitable for home assembly.